1. Field of the Invention
This invention relates to a method for reducing the frictional resistance of a navigating vehicle, and a method and an apparatus for generating micro-bubbles for reducing the friction in a low friction navigating vehicle. Especially, it is related to a technique of jetting micro-bubbles, composed of a mixture of air bubbles and water, out from the underwater surface of a ship, thereby reducing the frictional resistance as well as improving the overall energy utilization efficiency by making use of the dynamic energy of the mixture as a thrusting force.
2. Description of Related Art
There have been proposals for creating air bubbles or an air layer on the underwater surface of a ship for the purpose of reducing the friction of such ships.
Examples of the techniques for jetting bubbles into water are disclosed in prior art such as: (1) Japanese Patent Application, First Publication, S50-83992; (2) Japanese Patent Application, First Publication, S53-136289; (3) Japanese Patent Application, First Publication, S60-139586; (4) Japanese Patent Application, First Publication, S61-71290; (5) Japanese Utility Model Application, First Publication, S61-39691; (6) Japanese Utility Model Application, First Publication, S61-128185.
Also, a technique of forming an air layer in a concave part of the ship's bottom is disclosed in (7) Japanese Utility Model Application, First Publication, S61-128184.
These techniques are based on ejecting and blowing the pressurized air from a compressor through a plurality of holes or porous plates into the water.
However, with those methods based on jetting only pressurized air though a plurality of holes, it is difficult to obtain fine bubbles, and the buoyant air bubbles are easily separated from the underwater surface of the ship, resulting that the friction reduction is effective only in a narrow range of the surface. With the method based on porous plates, a large amount of energy is consumed in blowing air bubbles through the porous plate, generating a pressure drop through the plate, resulting that the consumption of energy used to blow out the bubbles is larger than the energy savings in reducing the fictional resistance. None of the techniques mentioned in prior art (1) through to (6) has matured into a practical technology. The technique disclosed in prior art (7) has also not come into practice, because it is thought that the large consumption of air needed for the technique is impractical.
This invention is presented in the view of such existing state of the present art, and has the following objectives:
1) To improve energy balance by reducing the frictional forces with low expenditure of energy, thereby effectively reducing the total energy consumption of a navigating vehicle; PA1 2) To develop a simple method for reducing the fictional resistance; PA1 3) To develop an effective technique for adjustments of air bubble mixing ratios and air bubble diameters to reduce the friction; PA1 4) To reduce the friction reliably without being affected by the shape of the ships; PA1 5) To simplify handling of air and water needed for reducing the friction; PA1 6) To develop an apparatus for reducing the friction which is simple to be installed in a ship.